1) Draw a circle with your finger tip on the fretted note. This will vary the pitch slightly.
2) Move your wrist closer then further away from the fretboard.
3) Rock your finger lengthwise on the fretted note. This is to change the volume of the note. (as far as I can tell, not really meant for bent notes).
Experiment with each method and vary the vibrato speed.
That's basically what the text says. Works for me, hopefully it helps you out.